1. Field of the Invention
The present invention relates to an optical lens system, and more particularly to a miniaturized optical lens system for taking image used in a camera mobile phone.
2. Description of the Prior Art
In recent years, with the popularity of camera mobile phone, the optical lens system for taking image has been becoming thinner and thinner, and the sensor of a general digital camera is none other than CCD (Charge Coupled Device) or CMOS (Complementary Metal Oxide Semiconductor). Due to advances in semiconductor manufacturing, the pixel size of sensors has been being reduced continuously, and miniaturized optical lens systems for taking image have increasingly higher resolution. Therefore, the demand for the image quality is increasing.
A conventional mobile phone's lens assembly usually consists of three lens elements: from the object side to the image side: a first lens element with positive refractive power, a second lens element with negative refractive power and a third lens element with positive refractive power, thus forming the so-called type of Triplet. To balance the light refractive power of the optical lens system, the optical lens system usually takes the form of “middle aperture stop”. However, the arrangement of middle aperture stop has the following disadvantages:
Firstly, a “middle aperture stop” type optical lens system requires a relatively long total optical length, which results in a relatively large mechanical structure, therefore, the middle aperture stop is inapplicable to a more miniaturized optical lens system for taking image.
Secondly, the exit pupil of the “middle aperture stop” type optical lens system is located closer to the image plane, making it more difficult for the optical designer to control light's incident angle on the sensor. In addition, “middle aperture stop” type optical lens systems inherently have pupil aberration which will increase the probability of the occurrence of vignetting.
The present invention mitigates and/or eliminates the afore-described disadvantages.